Semiconductor light emitting diodes are know to be highly sensitive to moisture. This sensitivity extends to exposure to chemicals, such as detergents and to mechanical stress. As a result, devices of this nature require encapsulation and protection by appropriate housing which, at the very least, provide appropriate electrical and optical interconnections.
Encapsulation and packaging of light emitting diodes should be simple and inexpensive on one hand, and reliable and durable, on the other. A variety of encapsulations for conventional semiconductor devices have been known to the art. Most of them are not well suited for light emitting diodes in view of their high mechanical complexity. Attempts have been made to reduce the complexity of the housing by using epoxy-like materials for hermetically sealing the diode.
An example of such an encapsulation package is described in the European Patent application, EP-A 0 466 975, "Semiconductor Light-Emitting Device". The principle governing the encapsulation of the light emitting device is schematically illustrated in FIG. 1. Shown is an edge emitting laser diode 10 mounted on a base 11 cube 12 with a 45.degree. mirror facet 13 positioned at a fixed distance from diode 10, thereby providing an optical output port. The laser diode 10 and the cube 12 are sealed and held in a transparent resin 14. The resin 14 adheres to the laser facets and fills the space between the laser 10 and the cube 12. The upper surface of cube 12 is not covered by resin 14. As shown by arrow 15, a light beam emitted from the laser 10 propagates through the resin 14, prior to its being reflected out of the resin.
The light emitting facet, referred to as mirror facet, is a critical element of a light emitting diode when addressing laser diodes. Because of the small emitting area (depending on the design of a light emitting diode), the optical flux density can be quite high (&gt;1 MW/cm.sup.2). Consequently, corrosion or contamination can easily lead to degradation of the output or melting of the light emitting facet through thermal runaway. Organic encapsulants, such as transparent resin (shown in FIG. 1), have all low thermal conductivity so that only a small degree of absorption can result in the presence of a local temperature rise. For this reason, most of the laser diodes are hermetically sealed in a metal enclosure which ensures that only an inert gas is in contact with the sensitive facets. A disadvantage of hermetically sealing light emitting diodes using an encapsulant is illustrated in FIG. 1. In it, the encapsulant adheres to the light emitting facet. Thus, it directly interacts with it and causes thermal problems if light beams with high optical flux density are to be generated. Furthermore, chemical changes in the encapsulant caused by high optical flux, can accelerate degradation (corrosion) of the facet.